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A guarantee of 2,000 workers at the end of this year was part of a deal made by the Legislature in 2011 as part of a package of incentives given to Amazon.

It's uncertain if a sales tax collection exemption given the company will continue once it expires at the end of 2015.

Amazon said it had 2,700 full-time workers at the two centers in a report to state and local officials in early October. "We know they've moved beyond that," Banning said.

The employment goal was reached a few months later than some officials hoped, but getting there is still welcome news.

"They're busting at the seams," said Randy Halfacre , president of the Greater Lexington Chamber of Commerce. "Despite the doubts, this is one of the best investments we've made."

Amazon's development is watched by area political and business circles since the company is one of the largest commercial projects to come to the Midlands in years.

The full- and part-time staff at the facility near Cayce exceeds 4,000 currently, forcing Amazon to rent parking space for workers at the State Farmers Market in nearby Dixiana and bus them to and from the center, officials say.

Its permanent staff there is around 1,800, officials say.

Some officials say Amazon has told them its staff, including temporary workers, is 5,500 statewide, more than the 4,500 first discussed.

The retailer is advertising for more temporary staff to handle a rush of orders from Christmas shoppers.

"We continue to hire in order to meet growing customer demand," Cheeseman said.

Amazon hasn't told Lexington County officials whether it will expand its center near I-77 and Old Wire Road. A site adjoining its center remains set aside for that possibility.

"The way that company is going, it would not surprise me if they want it," Banning said. "But there is no commitment."

One cloud on the horizon is the end of Amazon's tax collection exemption, a break that other retailers and the Tea Party wing of Republicans say gives it an unfair advantage.

Amazon has pressed for a national solution on taxation of Internet sales, but nothing has occurred.

The retailer is silent on whether it will seek to extend its tax break on goods sold to South Carolina residents beyond 2015.

State Rep. Kenny Bingham , a Cayce Republican, said there is an understanding in the 2011 deal that the retailer would be satisfied with that and not press for an extension. "The agreement was it would be one-time and then go away," he said.

But the company may not have to do anything to continue online sales untaxed for its in-state customers.

South Carolina's "mode of operation" is not to require taxation of merchandise from distribution centers if the company has no retail outlets here as is the case for Amazon, Bingham said.

The exemption given to it made sure no challenge would thwart the establishment of its new centers, he said.

Other retailers may seek again to make sure Amazon sales are taxed, creating "a very ambiguous situation," he said.

Amazon is required to send in-state customers an annual reminder of merchandise sold with a note that state sales tax is owed and should be added to state income tax payments.

Payment of those amounts is voluntary since state revenue officials aren't sent copies of those notices. Revenue officials say few taxpayers do so.

Another incentive given to Amazon is a fee that will be lower property taxes for 20 years on its $125 million center near Cayce that covers a million square feet on a 90-acre site.

Its bill this year is $1.4 million, up from $888,000 in 2012, records show.

The tax loss from the exemption is estimated at $2.5 million a year initially, but supporters say state and local coffers net $11 million a year initially from payroll and property taxes that the center near Cayce generates.